IRC
Internet Relay Chat , Basically a huge multi-user live chat facility. There are a number of major IRC servers around the world which are linked to each other.
Anyone can create a channel and anything that anyone types in a given channel is seen by all others in the channel. Private channels can (and are) created for multi-person conference calls.
IRC users can go into public or private channels to discuss a topic or transfer files. IRC servers are connected into networks. The most popular IRC client program is mIRC.
Many hosts are vary of letting customers access IRC because of a possibility of a denial of service attack on the whole network.